Go to Settings>Storage and see how much total internal storage it reports. Post a screenshot when you get a chance.

If it was formatted as internal storage, that means it's Adoptable Storage, and has been encrypted to be used only on that device. The problem with Adoptable Storage is that if the card is corrupt or unreliable (or if the phone's implementation of Adoptable Storage is buggy), then you might have difficulties saving data to it.

Oh, I see what you're saying -- the Apps, Videos, Images, etc. that are listed don't total to 7.27 GB. Does it seem reasonable to you that the card is actually full (i.e., do you have a lot of apps or data stored on the phone in general), or does it seem erroneous? I'm wondering if the phone is incorrectly showing the card as full, or incorrectly showing the contents (i.e., underreporting the size of the Apps, Videos, Images, etc.).

I'm not entirely sure why the phone is giving you that problem. As I mentioned before, it's possible that the firmware's implementation of Adoptable Storage is buggy. I'm not sure if you can easily move everything back to SD either if the card was formatted as Internal Storage. If you choose that Format as Portable option, I believe that will wipe the card, so that's not a good idea.

IMAP refers to the email client. But I'm not sure what those files are for. They might be intended to be temporary, because if you use the IMAP server of an email provider, the email app shouldn't be downloading emails directly to the phone's storage -- it should just be syncing with the server.